For a schoolboy watching the World Cup in 1978, the prospect of Scotland becoming world champions in Argentina couldn’t have seared more if had I been sirloin scorched on the parilla. While I’d never experienced anything like the disappointment of my country failing in their opening game against Peru, equally, I’d never seen anything like the goals installed at the tournament.

The white nets were beautiful but it was the black bands at the base of the posts that were the TV eye-candy. They drew the eye magnetically each time the goals came into camera shot. But why had they been painted on there? I knew this thought would itch until I scratched it.

It itched for nearly 40 years. By that time I had waded through a library of unsatisfactory books and TV documentaries that just missed the point. That was until I found myself accompanying my wife on her PhD research trip to Buenos Aires, where I met the man who painted the posts black – and explained why.

Unknown to my 10-year old self, in June 1978 Argentina was ruled by a murderous military junta. By the time of the World Cup finals, the junta had “disappeared” thousands of Argentinians, many into clandestine torture centres. I accompanied my wife as she researched the social memory of the junta’s violence, visiting these centres, and was struck by how many of them were in high-density urban areas.

One such clandestine torture centre was Club Atlético, so named because of its proximity to Club Atlético Boca Juniors stadium, La Bombonera. What was most striking about Club Atlético was its location in Buenos Aires CBD, the main commercial centre in the capital city. It was anything but clandestine. If the plan was to hide the torture centres, they were hidden in plain sight.

I took respite from the horror by visiting the rightly famous Don Julio parilla and the Plaza Italia book market, both of which are in Palermo, a leafy suburb in the north of the city. I was in the parilla pulling on a bottle of Quilmes beer while perusing a vintage full-colour picture book of the 1978 finals I’d scored at the market when a waiter approached and jutted out his chin in the universal code for “what are you reading?”

I showed him the photo, a full-page picture of French goalkeeper Jean-Paul Bertrand-Demanes lying injured at the base of the post in France’s group game against the hosts. The waiter – a tall, straight-backed elderly gentleman with a crooked smile – asked, in Spanish: “Are you French?”

I shook my head and explained, in my appalling Spanish, that the crumpled goalkeeper wasn’t my interest in the photo; the base of the post, painted black, was. He raised his eyebrows. Then, and was there a glint in his eye as he proceeded to take my order, he advised me that, if 1978 was my thing, I should visit Estadio Monumental, the site of the World Cup final.

I went to the Monumental a week later to watch River v Boca, the Superclásico: big noise, big colour and big spectacle. The game itself was a grinding, low-quality, goalless draw, which gave me plenty of time to ruminate how little the now-dilapidated stadium had changed since the 1978 World Cup final. The goal nets were now standard box-nets, same as the world over, and the black bands on the posts were long gone. Yet still, it would have been no surprise to see an Adidas Tango football drop from the sky and an apparition of Rob Rensenbrink appear near the six-yard line, stretching out a leg to divert the ball towards goal

The next day an Argentinian friend arranged for a stadium tour. When we walked on the pitch we roused the groundstaff who were languishing in the autumnal sunshine. I had managed slalom through the Dutch defence and was Mario Kempes bearing down on goal for 2-1 in the World Cup final when a burly, surly, slow-moving middle-aged groundsman approached, waving his hands. Like stadium staff everywhere, he wanted us off the grass.

“What happened to the old goal nets? They were beautiful,” I asked. The groundsman scratched his stomach and belched. I turned away from the goal then paused, drawing from the groundsman a sharp look that turned into a lazy shrug when I asked: “What about the black bands at the bottom of the posts?”

“A brush and black paint,” he answered impatiently. At this point I dug my heels in – literally dug my heels into the Monumental turf – and said: “Not how you painted the black bands. Why?”

After a deep sigh he looked at me, the fight ebbing out of him as he realised I’d travelled too far and obsessed over this question for too long to be pushed away. He escorted my friend and me to a poky, yellowed room that reeked of stale cigarettes and he gestured to the line of black and white photographs on the wall. I was, by now, accustomed to the collage of black and white portraits by which those who were disappeared by the junta in the 1970s were remembered.

The line of monochrome headshots on the stadium office wall looked no different but, as I approached the photos, I noticed in one picture a familiar crooked smile and glint of eye. “Who are these guys?” I asked. The groundsman shook a Marlboro out of a pack of 20 and explained that the men in the photos were the groundstaff who worked with the 1978 World Cup organising committee. “If you want to know why they painted the posts black, you’d have to ask these guys.”

I moved in close to the portrait that was somehow familiar, my heart beating in my ears. I concluded that, yes, the man in the photo was nearly 40 years younger with a wild, 1970s Leopoldo Luque hairstyle but the smile, the eyes – for sure, this was the waiter at the Don Julio parrilla. I pointed at the photo and asked his name. The groundsman blew a smoke ring and said: “Ezequiel Valentini.”

When I pushed on the door of Don Julio’s a week later, Ezequiel was pouring wine at table. He turned to look at me, recognition entering his eyes as a smile formed at the corners of his mouth, a quick nod communicating that he knew why I’d returned. At his afternoon break we sat at a table in the back, the sun angling in through the high window as he sipped on a Pepsi and told me why they had painted the base of the posts black in 1978.

“You have to understand,” he said in a low voice. “We had a big problem.” I edged closer as he explained that, while the groundstaff had a job to do, they were appalled at the idea of the junta exploiting the World Cup finals for political purposes and horrified by the disappearance of thousands of their compatriots.

“You knew about the disappeared?” I asked. “By mid-1978 everybody knew,” he replied. “The staff, the players, everyone had the same problem. How can we do our best knowing that the generals will benefit?” I remembered the old tale of the Argentina manager, César Luis Menotti, guiding his confused players through this moral maze before the final, advising them not to win for the junta but to win for the metal workers, the butchers, the bakers and the taxi drivers who filled the stadium.

Mario Kempes celebrates after scoring in the final at the Estadio Monumental. Photograph: Getty Images

“Already the goal nets had caused a lot of problems,” Ezequiel continued, saying Fifa had only two requests: that there be no stanchions or hardware behind the goal and that the method used to suspend the nets should be uniform throughout the six stadiums that were to host games. “We knew the nets would be on display for the whole world to see,” Ezequiel said. “It was important the method used to suspend the nets represented the people of Argentina.”

Both of Fifa’s requests were to prove difficult. “The stanchions were a part of regional or club identity,” Ezequiel said. “So replacing them was not going to be straightforward.” And what were the stanchions to be replaced with? Ezequiel leaned in, smiled his crooked smile and said: “You know us Argentinians consider ourselves more European than South American?” I’d heard this often, that as Simón Bolivar had not liberated Argentina from the Spanish, they were different to the other countries of Latin America. “So, naturally, we wanted a European method of suspending the nets.”

The ground staff were keen on the Continental Ds, or triangular elbows that had been prominent at Euro 76 in Yugoslavia but someone had caught the ear of an influential general and persuaded him that goal nets in South America had traditionally been suspended by L-supports, as seen at the World Cup in Brazil in 1950. Ezequiel shook his head at the absurd memory. “The junta was very keen on tradition. Whoever sold them the idea of Brazilian L-supports for a World Cup in Argentina knew exactly what buttons to press.”

The uniformity requested by Fifa proved problematic. “We’re just not a uniform people,” Ezequiel said, looking out the window and musing that, if the Argentinians were indeed European, they were southern European – Italian maybe, not German. The ground staff in Mendoza defied both Fifa and the junta to install “European” Continental D supports. Ezequiel shrugged, like, what can you do. “We’re just not a uniform people,” he repeated.

And what of the black bands at the base of the posts? Ezequiel touched his bicep and at once I realised: “They were black armbands? They were a protest against the disappearances?” They were not a protest. Rather, they were a form of remembrance.

“Everyone knew someone who knew someone that had been disappeared. The staff all wanted to protest. By now the Mothers were marching in Plaza de Mayo and we knew the world was watching. We discussed cutting a message into the grass, or painting a message on the advertising hoardings, something the TV cameras would see.”

The ideas were discarded. Publicly protesting against the junta in front of the world was akin to committing suicide. Ezequiel looked me in the eye. “I wasn’t scared for myself. The terror worked in such a way that made you scared for your family and friends. Every single player on each team at the World Cup should have publicly worn a black armband to remember the dead,” he said, jabbing the table with his finger.

With no safe opportunity to help the country protest, a colleague of Ezequiel’s mooted the idea of helping the country mourn. They decided the goalposts would be the public bearer of the black armband instead. First they had to present the idea to the generals. “They asked what the black bands were for. We told them it was tradition.” Ezequiel chuckled at the memory. “They were clueless about football.”

Were they worried that no one would know their exact purpose? Ezequiel shook his head. “Thousands were disappeared, presumed dead. Even today it is not possible to say exactly who and how many were killed by the junta. It was enough that they were remembered publicly.”

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I lean forward to press the point but Ezequiel is on a roll. “The junta sited their so-called clandestine torture centres in full view of the public. We remembered our dead in full view of the world. Like those centres, our act of remembrance was hidden in plain sight.”

The sun had long dipped behind the building opposite and Ezequiel had to get back to work. I thanked him for his time then signed my vintage Argentina 78 picture book and presented it to him as a memento of our time together. We shook hands and I got up to go.

Ezequiel shouted: “Wait.” I turned, confused. Did I forget something? Ezequiel cracked a warm, crooked smile and said: “Don’t you want to know if the Argentina v Peru match was fixed?”